1. Field of the Invention
The invention is directed to a system and methods for transmitting/receiving data during Broadcast mode and Multicast mode and, more particularly, to a system and method for reducing idle mode power consumption for mobile stations (MS) that have joined a Multimedia Broadcast/Multicast Service (MBMS) session and await the start of the session.
2. Detailed Description of the Related Art
MBMS (Multimedia Broadcast/Multicast Service) is a unidirectional Point-to-Multipoint (p-t-m) multicast/broadcast service in which data is transmitted from a single source entity to a group of users located in a specific area. MBMS may comprise a selection of unidirectional p-t-m bi-directional point-to-point (p-t-p) transmissions of multimedia data, such as text, audio, picture, or video, from a single source entity to a multiplicity of users in a service area. As stated in the 3rd Generation Partnership Project (3GPP) Technical Specification (TS) 22.146, “Multimedia Broadcast/Multicast Service; Stage 1”, it is a goal of MBMS is to allow the provision of multiple instances of a p-t-p service with a single transmission over a radio interface as a radio multicast. “Service area” for a given MBMS service is hereafter to be understood as the geographical area (i.e. set of cells) where the service is made available.
MBMS has two modes, e.g., Broadcast mode and Multicast mode. The main difference between these two modes is that in Broadcast mode all MBMS users in the service area are targeted for receipt of transmitted data, whereas in Multicast mode it is possible to address only a subset of the MBMS users in the service area for receipt of the data. As defined in the 3GPP TS 22.146, “Multimedia Broadcast/Multicast Service; Stage 1,” Multicast mode typically requires a user to subscribe to a multicast group before receiving the service.
As defined in the 3GPP TS 43.246, “MBMS in the Global System for Mobile communication (GSM) Enhanced Data GSM Environment (EDGE) Radio Access Network (GERAN); Stage 2”, a mobile station (MS) that has joined a paging group and has requested an MBMS session monitors an MBMS specific paging group for MBMS notifications. In order to permit the MS to save power by not reading all messages on the MBMS notification paging group, a single pre-notification bit (i.e., a flag) is sent on the primary paging group of the MS. This flag indicates that the MS must read the MBMS notification paging group or that the MS is not required to read the notification paging group. When the MS is not required to read the MBMS notification paging group, the network is permitted to send, instead of normal paging messages, other messages on the paging channel. In this case, however, it is not always possible to provide an indication of the status of the pre-notification flag. As a result, the MS is required to read the MBMS notification paging group even if a notification at that specific instant in time would not occur.
One problem with the prior art solutions for reducing MS power consumption, which is discussed in G2-MBMS04002 “Discussion paper: MBMS Pre-notification and Notification”, Ericsson 3GPP GERAN2 adhoc on MBMS, Turin, Italy, is that MBMS mobile stations may easily be required to read all MBMS specific paging group messages. This will occur if new MBMS sessions start frequently. Public land mobile network (PLMN) wide MBMS sessions need to be notified in all cells and location area wide MBMS sessions need to be notified in all cells of a location area. In addition, MBMS sessions intended for smaller areas to which a specific cell still belongs may exist. Moreover, MBMS sessions may occur even more frequently outside of busy periods when more network capacity would become available for downloading and recreational services, for example. In this case, frequent notifications are more likely to occur throughout any given day. In order to account for and process “lost” pre-notifications, the MS may be required to continuously read all MBMS specific paging group messages. If the discontinuous reception (DRX) period for an MBMS session is equal to the basic paging group of the MS, the power consumption of the MS will be increased by approximately 100%. Typically, the DRX period is used to minimize battery consumption in the MS. The DRX is defined using three parameters, i.e., DRX on/off, DRX period (paging group definition) and non-DRX timer, e.g., how long the MS stays in a non-DRX mode after the last transfer of data.
Another problem associated with the prior art solution for reducing MS power consumption is that MBMS sessions may be notified very frequently in a cell. As a result, an MBMS mobile station would be required to continuously read the MBMS paging group even if the pre-notification flag informs the MS about incoming notifications for MSMS sessions to which this particular MS has not joined.